Fecal sample starch content deteriorates over time after sampling
Dairy and beef cattle fecal samples are typically taken from commercial dairies and feedlots to assess starch utilization. Greater fecal starch content is related to lesser ruminal and total tract starch degradation and animal performance. Fecal sample starch concentration may change during time in transit to analysis laboratory, which in some cases can be five days or more. Dairy cattle fecal samples (at least ten 250g subsamples) were collected from manure piles at each of two commercial dairies in Wisconsin in July 2013. Subsamples were thoroughly mixed, immediately split on farm into air tight plastic containers (250g), and stored for 0 (control), 1, 2, or 5d. Samples stored for 1, 2, or 5d were also held at approximately 2C (cold), 22C (room), or ambient (variable, daily high 27C) temperatures. The 0h sample was processed on the same day samples were gathered. These combinations were organized in a factorial arrangement and chosen to simulate sample environment during shipping to analysis lab. Samples were oven dried (50C for 48h) and ground to 1mm following treatment. Starch content (% of DM) was measured in each sample and total tract starch digestibility (% of starch, TTSD) was calculated using the Ferraretto and Shaver 2012 equation: 100 X (0.9997 - 0.0125 × fecal starch). Data were analyzed with multiple linear regression using SAS JMPv10 and model effects chosen using forward selection. Temperature and time were entered as fixed effects and farm was random. Temperature (P<0.05) and time (P<0.01) were significantly related to fecal starch content and predicted TTSD. Fecal starch content averaged 4.3, 5.4, 4.3, and 4.1% for control, cold, room, and ambient temperature exposures, respectively. The numerically greater starch content at cold-storage temp relative to control was unexplained, and warrants further evaluation. Fecal starch content raw data averaged 5.4 and 3.7% at 0 and 5d, respectively. Predicted TTSD data averaged 93.3 and 95.4% at 0 and 5d, respectively. Model parameter slope estimates were -0.017 and 0.02 per h for fecal starch and TTSD, respectively. Results warrant further evaluation, but suggest fecal starch content and animal digestion estimates will change during extended time in transit. The amount of time between sampling and starch analysis should be considered and minimized.
Keywords: fecal, starch, digestion